While municipal water supplies are generally very good and provide acceptable quality drinking water, many home owners prefer to filter the main water supply in order to provide a safer, better tasting water in the home. Conveniently, such filtration equipment may be installed at the point of use under a sink near a faucet. The water supply is allowed to pass through a selected number of filter cartridges for removing sediment, dirt, rust and algae; to absorb objectionable taste, odours, colours and chlorine; and to reduce contaminants such as pesticides, and also to trap and kill harmful bacteria, cysts, and protozoa, as the case may be. Depending on the nature of the filter media used to treat the water, and the quality of the source water, it may become necessary to replace the filter on a periodic basis. In the case of a flow through water filter system, a convenient measure of when the filter media has reached its maximum capacity is to monitor the time during which the cartridge is in use. Alternatively, it is desirable to measure the volume of water being treated by the filter assembly.
For example, it is suggested by manufacturers that certain activated carbon cartridges be replaced typically every four months or six months depending on the cartridge and that a ceramic cartridge should be replaced every twelve months. It is however recognized that over a period of for example six months, different users will consume more or less water. It is therefore preferable to determine the volumetric throughput of the filter assembly and to change the filter media accordingly. For example, it is suggested that an activated carbon filter media should be replaced before a period of six months has expired if the throughput exceeds 600 gallons, failing which, the quality of the water may be adversely affected.
While water flow meters are generally well known, they are generally used by utility supply companies monitoring large volumetric flows. One of the problems which needs to be addressed in a domestic water supply environment is that the water volume throughput is intermittent at the point of use and may also have a very small flow rate. It then becomes challenging to provide accurate measurements of volume flow rate at a reasonable cost. Flow meters which incorporate a magnetized turbine are described in U.S. Pat. No. 3,053,087; U.S. Pat. No. 3,610,039; U.S. Pat. No. 5,372,048; and U.S. Pat. No. 5,876,610.
An object of this invention is to provide a fluid flow meter which is inexpensive to manufacture, which can reedily be incorporated into a conduit of a standard water filtration system and which will operate satisfactorily at the anticipated low flow rate prevalent in domestic water filtration units.